Why Richtext content is not searchable in hygraph/graphcms?

Im try to search content from the query user requested but hygraph not showing the result it only show data if title contains it…

export async function getServerSideProps(context) {
const { query } = context;
const { posts } = await hygraph.request(
    `
      query BlogPostPage($search: String! ){
            posts(where:{_search: $search}){
            createdAt
            id
            slug
            titile
            coverPhoto {
                url
            }
            content {
                html
            }
            author {
                name
                avtar {
                url
                }
            }
        }
      }
    `,
    { search: query.q }
);

return {
    props: {
        posts,
    },
};

}

i want this search query search the query from all the field how to do that ?